Optimized detector/modulator circuits are key components in passive microwave links which use smart labels and tags for identification and tracking of objects in shipping and transportation. The recent development of low-cost detector diodes and miniature antennas made it possible to develop electronic labels for the wireless supermarket and related applications requiring the use of inexpensive tags or smart labels serving as terminals in a modulated backscatter microwave link.
Our co-pending patent application, Ser. No. 08/380277, filed Jan. 30, 1995, and entitled "Wireless Electronic Module," teaches that the maximum sensitivity for the downlink (base station to label module) communication is achieved if the antenna port impedance is the complex conjugate of the diode impedance. While operating the antenna at such an impedance does improve downlink communications, it does not result in a maximum cross-section of a wireless label needed for efficient backscattering of an incident CW carrier to provide uplink (label to base station) communications.